Recently, electronic apparatuses have been developed with an increase in mounting density of components, in size and in various places for installation. The electronic apparatuses have been handled as precision devices and consideration have been given to the operating environment so far. However, it is expected that in the future the use of apparatuses in places where they have not been previously used will require that these apparatuses be able to withstand elements within the environment.
As an example, installation of large image display apparatuses in public places has been promoted. In order to display a lot of information on station platforms or in airports, there is an increasing need for image display apparatuses, such as liquid crystal types, instead of conventional image display apparatuses that use light emitting diodes (LED) or the like. The liquid crystal display apparatus includes liquid crystal and electronic components that are vulnerable to high temperature or dust. To address this problem, the long-term reliability of liquid crystal display apparatuses needs to be comparable to that of conventional image display apparatuses.
Due to the enhancement of product value brought by an increase in screen size and brightness, power consumption of the backlight used for a light source and of the power supply unit in the image display apparatus is increasing. Also, with enhancement of product performance due to voice function and the incorporation of a personal computer function into the image display apparatus, total power consumption of the image display apparatus tends to increase.
One of the element technologies that is required in order to achieve high reliability of the image display apparatus of this type, such as uniform image quality of the panel and long life, is a cooling technology that will satisfy temperature requirements that will ensure operation of a light source component, a control component and a power supply component. Unlike a liquid crystal display apparatus used as a home television set, an image display apparatus used in public places is typically operated continuously and is required to be resistant to elements within the environment depending on the place where the apparatus is installed. When used on a station platform or the like, the image display apparatus should not be vulnerable to electrically conductive dust or to a hot and humid environment. Further, the surface of a large liquid crystal panel cooled by natural convection tends to have a larger temperature difference between upper and lower parts as the size increases, and an excessive temperature difference impairs uniformity of image quality. Thus, cooling technology is needed for a large image display apparatus used in public places.
FIG. 1 is an exploded view of a liquid crystal display apparatus relating to the present invention. Components, such as fluorescent lamp 103 used as a backlight, are provided behind liquid crystal panel 102. Electrodes 104 and 105 are provided at both ends of the lamp, i.e., at both ends of the image display apparatus. Reflector 106 is provided in order to obtain uniform brightness. The temperature on the panel surface needs to be as uniform as possible because a variation in temperature on the surface of the liquid crystal panel causes a variation in light emission of the panel. For this purpose, a space is provided between liquid crystal panel 102 and back chassis 108 in order to obtain uniform brightness by the diffusion of light. Due to convection that occurs in the space, a temperature difference easily occurs particularly in the vertical direction. Thus, thermal diffusion sheet 107 using graphite etc. may be provided on reflector 106 on the side of the back chassis in order to promote thermal diffusion. The space starting from liquid crystal panel 102, located on the front surface, to thermal diffusion sheet 107 may be configured as a sealed structure which prevents dust or the like from entering therein from the outside in order to obtain stable and uniform brightness. When a liquid crystal display panel of the liquid crystal display apparatus using these components is cooled, it is important to cool the lamp, which is the major heat generating component inside the apparatus, while preventing direct contact with the outside air.
In general, this purpose is achieved by providing an intake port having a filter and an exhaust port for introducing ambient air at relatively low temperature into an image display apparatus and by cooling the light source component, the control component and the power supply component mounted in the apparatus with the ambient air. The filter on the intake port prevents entry of dust to some extent. However, this method regularly requires replacing of the filter. Further, fine dust enters an image display apparatus through the filter when the apparatus is installed in semi-outdoor public places. Electrically nonconductive and conductive fine dust floating in the outside air is deposited on the light source component, the control component and the power supply component in the apparatus. In particular, when electrically conductive dust enters the apparatus, a short circuit may occur between electronic circuit components mounted in the apparatus. Occurrence of a short circuit prevents improvement in reliability and causes a large problem in enhancing product value.
Thus, studies have been conducted to provide image display apparatuses that are excellent in dust resistivity and cooling performance and that are suitable for installation in semi-outdoor public places. For example, JP3975506B (hereinafter referred to as Patent Document 1) discloses an image display apparatus having a dust-proof container that houses a fluorescent lamp for a liquid crystal display panel. The container is formed by an image display unit on the front side and by a reflector on the back side. Air heated by the fluorescent lamp is led into square U-shaped ducts provided on both sides of the image display apparatus, is then cooled in the ducts, and then returned to the container. This arrangement provides a certain effect for satisfying requirements in which the apparatus will be able to withstand dust and in which the fluorescent lamp will be cooled.
JP2003-21823A and JP2004-294863A describe cooling technology for a liquid crystal panel and an image display apparatus having a power supply with high cooling performance, respectively.